﻿ Getting Started Tutorials - MechDesigner > Tutorial 14: Gear-Pairs / Rack-Pinions > Other Gear Configurations > Geared Four-Bar Mechanisms

# Geared Four-Bar Mechanisms

## Geared Four-Bar Mechanisms

Geared Four-bar Mechanisms are usually assembled with:

A four-bar mechanism, in which one Part rotates continuously.

One or two Gear-Pairs

The input gear is fixed to the Coupler, at the distal end of the Crank or the Rocker

The output gear is usually at the joint with the Base-Part of the respective Crank or the Rocker

Geared Four-Bar Mechanisms are often used as Function-Generators. Function-Generators provide an input to output mathematical relationship.

## Geared Four-bar Mechanism Configurations

### One Gear-Pair

Regressive and Ir-regressive Gears. (I do not know why they are called regressive and ir-regressive gears).

Regressive gears - a gear at each end of the Crank of a four-bar.

Ir-regressive gears - a gear at each end of the Rocker of a four-bar.

Note: Four-bar is a common term for a kinematic-chain with four Parts - usually with four Pin-Joints, usually one Part is the Base-Part.

#### Regressive Geared Four-bar

STEP 1: A Four-bar

Line-of-Centers

 The Line-of-Centers for the Regressive Gear-Pair is the CAD-Line in the Crank. The input to the Regressive Gear-Pair is the Coupler. The output from the Regressive Gear-Pair, is the Geared-Rocker. It is a new Part. The rotating axis of the Geared-Rocker (new Part)is at the rotating-axis of the Crank

STEP 2: Add the rotating-Part for the output of the Regressive Gear-Pair

 1.Kinematic toolbar > Add Part 2.Kinematic toolbar > Add Pin-Joint a.Click the start-Point of the new Part b.Click the Origin of the Crank

There are two Points at the origin of the Crank - the start-Point of the Crank, and the start-Point of the Line in the Base-Part.

The Select-Elements dialog opens because you have clicked three Points in total

STEP 2: Select two Points in the Select-Elements dialog

 1. CTRL+Click the start-Point of the new Part (Part4) + 2.CTRL+Click the start-Point of the Crank (Part) 3.Click to close the Select-Elements dialog

Why select the start-Point of the Crank?

The Line-of-Center is the CAD-Line in the Crank. The Pin-Joints be with Points at each end of the Line-of-Center.

STEP 4: Add the Regressive Gear-Pair

 1.Click Machine elements toolbar > Add Gear-Pair 2.Click the CAD-Line in the Coupler 3.Click the Cad-Line in the new free Part 4.Click the CAD-Line in the Crank 5.Click the dimension Line that defines the length of the Crank 6.Click in the Command-Manager

STEP 5: Edit the Gear-Pair

If you do not want to change the length of the Crank, do not change the total number-of-teeth.

STEP 6: Plot a Graph of the Output vs the Rotation of the Crank

Add a Measurement FB to measure the motion of the Geared Rocker - the Output-Gear

#### 'Ir-regressive' Geared Four-bar

STEP 1: A Four-bar

Line-of-Centers

The Line-of-Centers for the Regressive Gear-Pair is the CAD-Line in the Crank.

The input to the Regressive Gear-Pair is the Coupler.

The output from the Regressive Gear-Pair, is the Geared-Rocker. It is a new Part.

The rotating axis of the Geared-Rocker (new Part)is at the rotating-axis of the Crank

STEP 2: Add the rotating-Part for the output of the IR-Regressive Gear-Pair

 1.Kinematic toolbar > Add Part 2.Kinematic toolbar > Add Pin-Joint a.Click the start-Point of the new Part b.Click the Origin of the Rocker

There are two Points at the origin of the Rocker - the start-Point of the Rocker, and the end-Point of the Line in the Base-Part.

The Select-Elements dialog opens because you have clicked three Points in total

STEP 3: Select two Points in the Select-Elements dialog

 1. CTRL+Click the start-Point of the new Part (Part4) + 2.CTRL+Click the start-Point of the Rocker (Part) 3.Click to close the Select-Elements dialog

Why select the start-Point of the Rocker?

The Line-of-Center is the CAD-Line in the Rocker. The Pin-Joints be with Points at each end of the Line-of-Center.

STEP 4: Add the Regressive Gear-Pair

 1.Click Machine elements toolbar > Add Gear-Pair 2.Click the CAD-Line in the Coupler 3.Click the Cad-Line in the new free Part 4.Click the CAD-Line in the Crank 5.Click the dimension Line that defines the length of the Crank 6.Click in the Command-Manager

STEP 5: Edit the Gear-Pair

 If you do not want to change the length of the four-bar Rocker, do not change the total number-of-teeth.

STEP 6: Plot a Graph of the Output vs the Rotation of the Crank

 1.Add a Measurement FB to measure the rotating motion of the Geared Rocker - the Output-Gear 2.Add a Graph FB 3.Connect wires from the Measurement FB to the Graph FB.